Effect of microwave heating on the solid state reactions and mass transport in ceramics

The use of microwave energy to process a wide range of ceramic materials offers an alternative to the conventional heating of ceramics. With microwave energy, heat generation is internal and volumetric, making it possible to rapidly and uniformly heat even large ceramic bodies. Conventional heating is carried out by placing the ceramics in furnaces with external heat sources. Heating of ceramics is completely dependent on the thermal conductivity of the material. Unfortunately, most ceramics are poor thermal conductors and can not be heated rapidly.;Microwave processing has so far been mainly focused on the sintering of ceramics and composites. The reduction in processing time and temperature (higher sintering rates) has resulted in a common speculation of higher diffusion rates with microwave heating.;This research is concerned with the effect of microwave heating on solid state reaction between zinc oxide and aluminum oxide. The reaction between zinc oxide and aluminum oxide has been reported to be diffusion controlled and it proceeds only on the alumina particle by one-way transfer of zinc oxide through the product layer. If microwave heating results in enhanced diffusion, it should enhance the reaction rates of zinc oxide and aluminum oxide.;It has been demonstrated in this work that microwave heating results in more product formation with large particles of alumina reacting with zinc oxide. The reaction of zinc oxide with polycrystalline and single crystal alumina also results in larger thickness of product layer with microwave heating. However, with a small particle size of alumina conventional heating resulted in more product formation at lower temperatures, which needs further investigation.